Mold Oscillation Research Articles

Mathematical Modeling of Initial Solidification and Slag Infiltration at the Meniscus of Slab Continuous Casting Mold

In the current study, a mathematical model was established to investigate meniscus solidification and slag infiltration in the mold. The model considered the two-dimensional steel-slag-air three-phase fluid flow, heat transfer, solidification of the steel and mold oscillation. The calculated solidification shell was compared with measured hook lines to validate the model. The initial solidification and slag infiltration at the meniscus were revealed during an oscillation cycle. The influence of casting parameters on initial solidification was studied. Through simulations, the liquid slag flowed into the gap between the steel shell and copper plate during the positive strip stage, while it flowed out of the gap during the negative strip stage. The solidification depth of the meniscus from the solidification tip to the inner mold face reduced with the increase of casting temperature and casting speed and the decrease of water flow rate in the mold and oscillation amplitude.

Mold Simulator Study of Effect of Mold Oscillation Frequency on Heat Transfer and Lubrication of Mold Flux

Mold Simulator Study of Effect of Mold Oscillation Frequency on Heat Transfer and Lubrication of Mold Flux

Study of Mold Oscillation Parameters and Modes on Slag Lubrication in Slab Continuous Casting

The effects of mold oscillation parameters and modes on slag lubrication were quantified based on a verified multi-phase model for liquid slag infiltration during continuous casting. The main results indicated that the variations of slag film thickness, slag consumption, and heat flux at the meniscus were generally periodic with the mold oscillation. For sinusoidal oscillation, shorter amplitude or lower frequency consumed much more liquid slag. Non-sinusoidal mode could increase the slag consumption from 0.274 kg/m2 to 0.286 kg/m2, an approximately 4.4% increase over that of the conventional mode. The evolution of heat flux at the meniscus fluctuated severely with lower oscillation frequency, while the non-sinusoidal mode was stable, approximately 1.6 MW/m2. This study demonstrated that the positive strip time contributed more to lubrication than the negative strip time and that the slag consumption decreased with an increase of negative strip ratio in mold oscillation.

Effect of Shear Stress on Isothermal Crystallization Behavior of CaO-Al₂O₃-SiO₂-Na₂O-CaF₂ Slags.

How to coordinate the contradiction between lubrication and heat transfer in the peritectic steel casting process is the key technical difficulty in preparing mold fluxes. The mold fluxes that are required for casting are subjected to the shear stress generated by mold oscillation and slab movement, which affects the crystallization performance of slags. The quantitative effect of slags’ crystallization performance by shear stress is studied to develop a low-basicity and high-crystallization mold flux to solve the above problem. The results show that the crystallization kinetic condition is promoted, and the crystallization activation energy is reduced by the shear stress, which leads to an increase in the crystallization temperature. Concurrently, the crystal size is reduced. However, the shear stress has no effect on the crystalline phase. The influence of different shear stresses on the crystallization ability of molten slags is related to the crystal nucleation and growth mechanisms. The crystalline fraction of the slag films at 300 rpm (69 s−1) is 44.7%, which is an increase of 17.7% compared with the crystalline fraction of the slag films at 200 rpm (46 s−1). Moreover, the shear stress has little effect on the lubricating properties of the mold fluxes, although the crystallization ability is promoted by the agitation.

Study of the Mechanism of Liquid Slag Infiltration for Lubrication in Slab Continuous Casting

Consistent and uniform lubrication of the solidifying shell, especially in the meniscus, is crucial for the smooth continuous casting operation and production of strands free of surface defects. Thus, the current study established a coupled model to study the inflow behavior of liquid slag to the mold-strand channel, taking the solidification of steel and slag and the periodic oscillation of mold into account. The difficulties and solutions for the simulation were described in detail. The predicted profiles of the slag rim and initial shell were in good agreement with the reports. The main results indicated that liquid slag could be squeezed out and back into the slag pool in a negative strip period while a large amount of liquid slag could infiltrate into the mold-strand channel. Thus, the amount of slag consumed in the negative strip period was relatively small compared with that in the positive strip period. The predicted variation of slag consumption during mold oscillation was periodic, and the average value was 0.274 kg/m2, which agreed well with the slag consumption in industrial practice. The current model can predict and optimize the oscillation parameters aiming at stable lubrication conditions.

Analysis of Meniscus Fluctuation in a Continuous Casting Slab Mold

A water model of slab mold was established to analyze the microscopic and macroscopic fluctuation of meniscus. The fast Fourier transform and wavelet entropy were adopted to analyze the wave amplitude, frequency, and components of fluctuation. The flow patterns under the meniscus were measured by using particle image velocimetry measurement and then the mechanisms of meniscus fluctuation were discussed. The results reflected that wavelet entropy had multi-scale and statistical properties, and it was suitable for the study of meniscus fluctuation details both in time and frequency domain. The basic wave, frequency of which exceeding 1 Hz in the condition of no mold oscillation, was demonstrated in this work. In fact, three basic waves were found: long-wave with low frequency, middle-wave with middle frequency, and short-wave with high frequency. In addition, the upper roll flow in mold had significant effect on meniscus fluctuation. When the position of flow impinged was far from the meniscus, long-wave dominated the fluctuation and the stability of meniscus was enhanced. However, when the velocity of flow was increased, the short-wave dominated the meniscus fluctuation and the meniscus stability was decreased.

Estimation of Lubrication and Heat Transfer by Measurement of Friction Force in Mold

In the continuous casting process of steels, the mold flux infiltrated in between a mold and solidified shell plays an important role to optimize lubrication and heat transfer to establish not only stable operation but also good surface quality of slabs. Therefore, lubrication and heat transfer was evaluated by measuring friction force attributed to the mold oscillation along with a lubrication model. The friction force was measured with a slab caster equipped with hydraulic oscillators, to understand how the friction force was affected by continuous casting factors such as the mold oscillation conditions, mold flux properties and casting speed.

A coupled model on fluid flow, heat transfer and solidification in continuous casting mold

Fluid flow, heat transfer and solidification of steel in the mold are so complex but crucial, determining the surface quality of the continuous casting slab. In the current study, a 2D numerical model was established by Fluent software to simulate the fluid flow, heat transfer and solidification of the steel in the mold. The VOF model and k-e model were applied to simulate the flow field of the three phases (steel, slag and air), and solidification model was used to simulate the solidification process. The phenomena at the meniscus were also explored through interfacial tension between the liquid steel and slag as well as the mold oscillation. The model included a 20 mm thick mold to clarify the heat transfer and the temperature distribution of the mold. The simulation results show that the liquid steel flows as upper backflow and lower backflow in the mold, and that a small circulation forms at the meniscus. The liquid slag flows away from the corner at the meniscus or infiltrates into the gap between the mold and the shell with the mold oscillating at the negative strip stage or at the positive strip stage. The simulated pitch and the depth of oscillation marks approximate to the theoretical pitch and measured depth on the slab.

Recovery mechanism of the sticking-type breakout during continuous casting of steel

ABSTRACTSticking-type breakout is one of key factors which restrict the development of high-speed or wide-heavy plate continuous casting technology. In order to better heal and control the sticking-type breakout, this paper presents a comprehensive study for its recovery mechanism. First, according to force characteristics of solidified shell at mold exit, calculation method of safe shell thickness is proposed. Then, considering sticker propagation behaviour and safe shell thickness, a more practical recovery model of sticking-type breakout is established and verified by actual examples. The result shows the proposed recovery strategies avoid casting speed to be decreased too low or cast stop, thus save unnecessary operating time, and are better than original strategies. Furthermore, influencing factors of recovery behaviour are analyzed. The result shows hot spot location, operating casting speed, and mold oscillation frequency have a significant effect on minimum speed for the recovery and oscillation stoke has little influence on it.

Effect of mold oscillation on the metallurgical characterization and mechanical properties of A319 aluminum alloy casting

Effect of mold oscillation on metallurgical characterization and mechanical properties of the A319 alloy was investigated. Experimental results show that the microstructure of A319 alloy was significantly refined regarding α-Al grain refinement along with improved silicon particle morphology due to mold oscillations. Mechanical properties of casting such as tensile strength, yield strength, percentage elongation and micro-hardness improved by 39.05, 28.05%, 2.67 times and 27.02% respectively as compared to that of stationary casting. This investigation is an attempt to study the effect of mold frequency on mechanical and metallurgical properties of aluminum alloys.

Review of the Control Parameter for Hydraulic Mold Oscillation in Continuous Casters

Review of the Control Parameter for Hydraulic Mold Oscillation in Continuous Casters

Mechanism analysis of non-sinusoidal oscillation of continuous casting mold synchronously driven by double servomotors

Due to the disadvantages of complexity, high maintenance and vast investment of the electro-hydraulic servo oscillator, a new mechanical device synchronously driven by double servomotors was proposed. The working principle of the non-sinusoidal oscillator was analyzed and the model of the oscillator was validated via simulation software. Then, taking advantage of resonance technology, the hinging force and moment were calculated. The results showed that the hinging force and driving moment reduced, which was useful in reducing the impact of the hinge and prolonging the service life of the bearing. Besides, the best initial spring pressure was 0.9 times the mold gravity, which improved the oscillation system stability and reduced the load fluctuation and servomotor driving power.

Metallurgical and Mechanical characterization of A319 Aluminum Alloy Casting Solidified Under Mold Oscillation

This paper deals with the effect of mold oscillation (during alloy solidification) on the metallurgical and mechanical properties of A319 alloy casting. For the evaluation of aforesaid effect, oscillatory amplitudes of 5, 10, 15, and 20 µm with a constant frequency of 100 Hz were used. Results obtained under oscillatory conditions were compared with those of castings prepared under stationary condition. Metallurgical properties were examined through microstructure, tensile fracture SEM and SEM image of test specimens prepared under different conditions of solidification. Grain refinement was obtained through mold vibration. SEM image of the tensile fractured surface in all the cases reveals a mixed mode of fracture consisting of fine dimples and intergranular decohesion fracture surfaces. Small dimples indicate that some plastic deformation has taken place before fracture. Cleavage formation may be attributed to the presence of hard and brittle Al2Cu and FeSi phases. Likewise, mechanical properties of oscillatory casting were examined through the tensile and microhardness test and compared with similar properties obtained under stationary condition.

Mold Oscillation Feedforward Control Algorithm for Sinusoidal Oscillation of Various Asymmetries

Mold Oscillation Feedforward Control Algorithm for Sinusoidal Oscillation of Various Asymmetries

Oscillation-Mark Formation and Liquid-Slag Consumption in Continuous Casting Mold

Traditional understanding on the complex multiphysics phenomenon of the meniscus in the oscillating mold for continuously cast steel, including oscillation-mark formation and liquid-slag consumption, has never considered the shape influence of the flux channel between the mold wall and the solidifying shell surface. Based on the reciprocating oscillation of mold, this study was carried out to calculate theoretically the periodic pressure and the liquid-slag layer thickness in the flux channel for the upper and the lower meniscus that possess different shapes in combination with a transient equilibrium profile of the flux channel as well as the sinusoidal and the nonsinusoidal oscillation modes of mold. The effect of flux channel shape on the multiphysics phenomenon in the meniscus was determined by the physical oscillation simulation by using an experimental cold model mold. The results show that the shape difference between the upper and the lower meniscus leads to the opposite direction of pressure in the flux channel. The pressure in the opposite direction plays a respective role in oscillation-mark formation and liquid-slag consumption in an oscillation cycle of mold, and thus, it makes a new mechanism for explaining the multiphysics phenomenon in the meniscus. The oscillation mark is initially formed by the rapid increase of positive channel pressure in the upper meniscus, and most of the liquid slag is infiltrated into the flux channel by the negative channel pressure in the lower meniscus from the end of a positive strip time to the beginning of the next positive strip time, including the negative strip time in between. Furthermore, the physical characteristics of the lubrication behavior in the meniscus are summarized, including liquid-slag infiltration, solidifying shell deformation, and the thickness change of the liquid-slag layer.

The system of estimation of the state variables for PWM converter control in the structure of mold oscillation mechanism

The control system of PWM converter in hydraulic drive structure of the mold oscillation mechanism is used for prevent distortions of the mold movement. It is based on collecting data from accelerometers. This system can be useful for many metallurgical plants of Ukraine and overseas where continuous casting technology is used.

Mold Simulator Study on the Initial Solidification of Molten Steel Near the Corner of Continuous Casting Mold

Corner cracks are one of the most widespread surface defects of continuous casting slabs, and they are especially severe for peritectic steels and low-alloy steels. Therefore, a clear understanding of molten steel initial solidification around mold corner would be of great importance for the inhibition of corner cracks. This paper has been conducted with the aim to elucidate this understanding, by using a novel mold simulator equipped with a right-angle copper mold. The responding temperatures and heat fluxes across the mold hot-face and corner were firstly calculated through a 2D-inverse heat conduction program mathematical model, and the results suggested that the cooling ability and the fluctuation of heat fluxes around the mold corner are stronger than those for mold hot-face. With the help of power spectral density analysis and fast Fourier transformation, the four characteristic signals of heat fluxes were discussed in this paper. Next, the relation between the thickness of solidified shell and solidification time was fitted with the solidification square root law; as a result, the average solidification factor \( \bar{K} \) for the hot-face shell is 2.32 mm/s1/2, and it is 2.77 mm/s1/2 for the shell near-corner. For the same oscillation marks (OMs), it appeared that the OMs positions on the shell corner are lower than those on the shell hot-face along the casting direction, because the stronger shrinkage of shell at the corner allows the overflowing steel to penetrate deeper into the larger gap between the shell corner and mold, which is demonstrated through the heat transfer analysis and metallographic examination. Finally, the interrelation between shell profile, mold oscillation, variation rate of heat flux, high-frequency heat flux and high-frequency temperature was discussed for above two cases, and the results suggested that meniscus conditions (heat transfer and melt flow) around the mold corner are more unsteady.

Dynamic Response of Mold Oscillator Interacting with Steel Slabs

A mathematical model to show the dynamic response of the mold oscillator was suggested. The model considered a frictional interaction between the mold oscillator and slab as several connected nodes. The governing equation considered the slab as a multi-degree-of-freedom (DoF) system, and included a hysteresis model to describe elastic-plastic behavior of the slab; the mold oscillator was given two DoF by utilizing pressure and displacement experiment data. Simulations indicate that the mold and slab execute various vibrations, and that mold oscillation marks are caused by a stick-and-slip phenomenon during intervals, in which the slab contacting the mold moves downward compared to the other slab (negative strip time). The slab shows the formation of mold oscillation marks to previous formation criterion equally when the mold velocity is faster than the casting speed about downward. The oscillation mark will grow up over 2 Hz exciting frequency with constant 4 mm stroke in simulations. Finally, the negative strip time was compared to the frictional force, hysteresis variable, and plastic force to investigate formation mechanism of the oscillation marks.

Modeling and verification of the nonlinear system of oscillation platform of continuous casting mold driven by servo motor

The driving mode by servo motor is a new driving mode and can realize oscillations of continuous casting mold as expected. The oscillation system of continuous casting mold driven by servo motor is a complicated nonlinear system. Therefore, it is necessary to establish an accurate model for the system before performing simulation experiments. Based on the oscillation platform system of continuous casting mold driven by servo motor in the laboratory, the nonlinear models of servo motor speed system and mechanical transmission parts were respectively established and the viscous friction coefficient, moment of inertia, and load torque were identified. Then, the nonlinear mathematical model of the whole oscillation platform of continuous casting mold driven by servo motor was obtained. The comparison results between the simulated output curves of established model and the measured output curves of actual system under the same input signals indicated that the simulated curves were almost in accord with the measured curves. Therefore, the proposed model can reflect the capabilities of practical system and lay a good foundation for subsequent research on simulation experiments and accurate control of continuous casting mold oscillation driven by servo motor.

Mold Simulator Study of the Initial Solidification of Molten Steel in Continuous Casting Mold: Part II. Effects of Mold Oscillation and Mold Level Fluctuation

The surface quality of the continuous casting strands is closely related to the initial solidification of liquid steel in the vicinity of the mold meniscus, and thus the clear understanding of the behavior of molten steel initial solidification would be of great importance for the control of the quality of final slab. With the development of the mold simulator techniques, the complex interrelationship between the solidified shell surface profile, heat flux, shell thickness, mold level fluctuation, and the infiltrated slag film was well illustrated in our previous study. As the second part, this article investigated the effect of the mold oscillation frequency, stroke, and mold level fluctuation on the initial solidification of the molten steel through the conduction of five different experiments. Results suggested that in the case of the stable mold level, the oscillation marks (OMs) exhibit equally spaced horizon depressions on the shell surface, where the heat flux at the meniscus area raises rapidly during negative strip time (NST) period and the presence of each OMs on the shell surface is corresponding to a peak value of the heat flux variation rate. Otherwise, the shell surface is poorly defined by the existence of wave-type defects, such as ripples or deep depressions, and the heat flux variation is irregular during NST period. The rising of the mold level leads to the longer-pitch and deeper OMs formation; conversely, the falling of mold level introduces shorter-pitch and shallower OMs. With the increase of the mold oscillation frequency, the average value of the low-frequency heat flux at the meniscus increases; however, it decreases when the mold oscillation stroke increases. Additionally, the variation amplitude of the high-frequency temperature and the high-frequency heat flux decreases with the increase of the oscillation frequency and the reduction of the oscillation stroke.